The role of the water molecules in novel superconductor, Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O

TL;DR

This study investigates how water molecules influence superconductivity in Na$_{0.35}$CoO$_{2}$·1.3H$_{2}$O by comparing magnetic susceptibilities with a non-superconducting variant, suggesting water's role in shielding Coulomb potential and enabling superconductivity.

Contribution

It provides experimental evidence that water molecules in Na$_{0.35}$CoO$_{2}$·1.3H$_{2}$O help facilitate superconductivity by modifying the electronic environment.

Findings

Superconducting Na$_{0.35}$CoO$_{2}$·1.3H$_{2}$O shows enhanced susceptibility below 150 K.

Non-superconducting Na$_{0.35}$CoO$_{2}$·0.7H$_{2}$O does not show this enhancement.

Water molecules may shield Coulomb potential, promoting superconductivity.

Abstract

In order to investigate the role of the water molecules in Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O, we synthesized superconducting Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O and nonsuperconducting Na$_{0.35}$CoO$_{2}\cdot$0.7H$_{2}$O, and measured their normal-state magnetic susceptibilities. The susceptibility of Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O has an enhancement below ~150 K probably caused by ferromagnetic fluctuation, whereas no such enhancement was observed in Na$_{0.35}$CoO$_{2}\cdot$0.7H$_{2}$O. The water molecules in Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O may work to shield random coulomb potential of the Na ions with smoother potential at the CoO$_{2}$ layer. This effect may account for the appearance of superconductivity in Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O.